Process for the Epoxidation of a Tetrasubstituted Alkene

ABSTRACT

This invention relates to a process for the epoxidation of a tetrasubstituted alkene such as terpinolene to the corresponding epoxide such as terpinolene epoxide by reacting the tetrasubstituted alkene with peracetic acid prepared in situ from acetic anhydride and hydrogen peroxide in the presence of at least one buffering agent. Further, the invention relates to the use of an oxidizing agent comprising hydrogen peroxide and acetic anhydride for the in-situ epoxidation of a tetrasubstituted alkene.

This invention relates to a process for the epoxidation of a tetrasubstituted alkene such as terpinolene of the formula (Ia) to the corresponding epoxide such as terpinolene epoxide of the formula (IIa).

Because of its wide utility, the epoxidation of alkenes is important on an industrial scale. Tetrasubtituted olefins are common structural units in many classes of compounds, particularly natural products. Their corresponding epoxides are useful as intermediates for producing compounds used in various final applications such as in the pharmaceutical, agricultural and fine chemical industries.

For example, terpinolene epoxide is a valuable intermediate in the synthesis of terpinene-4-ol—an unsaturated tertiary terpene alcohol that occurs naturally in a number of essential oils. Terpinene-4-ol finds use as a component in synthetic essential oils which are compounded for use as flavors or perfumes. Because of high costs and uncertainty of supply of the natural product, synthetic routes to terpinene-4-ol have been developed, e.g. via epoxidation route starting from epoxidation of terpinolene. Nevertheless, there is still room for improvement with regard to the epoxidation step.

U.S. Pat. No. 3,676,504 describes a process for the preparation of terpinolene epoxide by epoxidation of terpinolene by using an organic peroxy acid, such as peracetic, perpropionic or m-chloroperbenzoic acid as oxidizing agents. The exemplified epoxidation of terpinolene makes use of a preformed 40% solution of peracetic acid as oxidizing agent. It is known that some of the preformed, in particular highly concentrated peroxy acid solutions are unstable, and cannot be safely stored or handled. Since peroxy acids can decompose spontaneously under explosion due to thermal or mechanical stress and their reactions are often highly exothermic, specific safety measures such as e.g. proper cooling and dilution are required during the course of the reaction. This leads to a low space-time yield and makes such reactions not very suitable for an industrial scale preparation. The reaction is effected in a halogenated organic solvent (i.e. methylene chloride). However, the use of such halogenated solvents has the disadvantage that the production wastewaters contain hazardous AOX (adsorbable organic halogen compounds) which is undesirable from an environmental point of view.

U.S. Pat. No. 3,130,207 describes process of epoxidizing various olefinic compounds by reacting said olefinic compounds with a preformed liquid aliphatic peroxy acid solution comprising a substantial equilibrium mixture of liquid aliphatic peroxy acid, liquid aliphatic acid, hydrogen peroxide, and water, and adding a liquid aliphatic acid anhydride to react preferentially with the hydrogen peroxide present in the equilibrium mixture to form additional liquid aliphatic peroxy acid. The exemplified olefinic compounds contain double bonds which are not more than disubstituted. Further, the exemplified epoxidation reactions make use of a preformed 40% solution of peracetic or perpropionic acid as oxidizing agent and acetic anhydride as the liquid aliphatic acid anhydride. The same disadvantages associated with the use of preformed peroxy acid solutions as outlined hereinabove equally apply to this process. Further, the anhydride should not be added directly to the concentrated peroxy acid mixture, because the anhydride would violently react with the equilibrium mixture. Since the reaction between the anhydride and the hydrogen peroxide is exothermic, an additional step of adding the anhydride in increments is recommended after the peroxy acid has been added.

Kleschnik W. A. et al, Synthesis, Vol. 1997, No. 07, July 1997, pages 783-786 describes the use of a mixture of acetic anhydride, Na₂HPO₄ and urea-H₂O₂ in methylene chloride in the epoxidation of benzyl 3-methylnorbornene-2-carboxylate (10) to yield 2-benzyloxycarbonyl-3-methylexo-2,3-epoxynorbornane (11).

Cooper M. S. et al, Letters, September 1990, pages 533-535 describes the epoxidation of certain alkenes (e.g. α-methylstyrene and cyclohexene) using urea-hydrogen peroxide (UHP) in combination with acetic anhydride in the presence of disodium hydrogen phosphate and dichloromethane.

One major disadvantage of the combined use of urea-hydrogen peroxide (UHP) and carboxylic anhydrides such as acetic anhydride as described in the aforementioned epoxidation methods lies in that high concentrations of highly explosive diacyl peroxides may be formed. The authors do not recommend the use of such mixtures of UHP and carboxylic anhydrides (e.g. acetic anhydride) except when UHP is present in large excess in chlorinated solvents such as dichloromethane. However, neither large excess amounts of UHP nor halogenated solvents are desirable from an economical or environmental point of view.

Further references (cf. Heteroatom Chemistry, Volume 12, Number 3, 2001, pp. 119-130; Russian Journal of Organic Chemistry, Vol. 37, No. 11, 2001, pp. 1564-1569; Russian Journal of Organic Chemistry, Vol. 38, No. 2, 2002, pp. 165-175; Russian Journal of Organic Chemistry, Vol. 40, No. 10, 2004, pp. 1415-1426 and Tetrahedron 63, 2007, pp. 1790-1797) describe the in-situ epoxidation of specific disubstituted alkenes, especially norbornene derivatives, with hydrogen peroxide of acetic anhydride in the presence of a base and a halogenated organic solvent (chloroform). Disadvantages of these processes are, for example, those associated with the use of a halogenated organic solvent as described above. Further, all reactants like hydrogen peroxide (H₂O₂), acetic anhydride and bases are employed in high excess which is unfavorable from an economical and ecological point of view. In addition, highly concentrated aqueous solutions of H₂O₂ (70% and 90%) are necessary in some examples to achieve high yields. However, the use of higher concentrations of H₂O₂ (e.g. greater than 70%) poses serious hazard problems due to the increased susceptibility to decomposition.

In view of the above drawbacks, there is still need for improved methods for the epoxidation of tetrasubstituted alkenes, in particular terpinolene (Ia), which would not only make the process safe and environmentally friendly, but also would be simple and cost-effective for commercial utilization.

It is therefore an object of the present invention to overcome or ameliorate at least one of the above disadvantages and thus to provide an improved and more economically and commercially feasible process for the epoxidation of tetrasubstituted alkenes, in particular terpinolene (Ia).

Another object is to provide an industrially simple process for the epoxidation of tetrasubstituted alkenes, in particular terpinolene (Ia), which gives the corresponding epoxides, in particular terpinolene epoxide (IIa), in good yields.

A further object is to provide a more environmentally friendly process for the epoxidation of tetrasubstituted alkenes, in particular terpinolene (Ia), by reducing unfavorable environmental effects.

Still another object is to provide an industrially feasible process for the epoxidation of tetrasubstituted alkenes, in particular terpinolene (Ia), which reduces safety concerns and the existence of hazardous conditions.

Yet another object is to provide a process for the epoxidation of tetrasubstituted alkenes, in particular those containing at least one (preferably one or two and more preferably one) additional carbon-carbon double bond (the additional carbon-carbon double bond preferably being disubstituted or trisubstituted, more preferably trisubstituted) such as, for example, terpinolene (Ia) which results in a higher selectivity towards the epoxidation of the tetrasubstituted double bond while reducing the formation of undesirable by-products.

It has now surprisingly been found that these and further objects are, in part or in whole, achieved by a process for the epoxidation of a tetrasubstituted alkene to the corresponding epoxide comprising reacting the tetrasubstituted alkene with peracetic acid prepared in situ from acetic anhydride and hydrogen peroxide in the presence of at least one buffering agent.

Accordingly, the aforementioned process for the epoxidation of a tetrasubstituted alkene is a subject matter of the present invention.

The process according to the present invention entails a series of advantages and overcomes drawbacks of the prior art processes.

The process of this invention avoids the handling of preformed peroxy acid solutions thus minimizing the risk of explosions while maintaining efficiency and ease of operations. The in-situ preparation of peracetic acid from acetic anhydride and hydrogen peroxide allows the epoxidation of the tetrasubstitued alkene to proceed in a smooth and controlled manner, which is very safe, simple, economical, user-friendly and commercially viable.

Further, the process of this invention uses a relatively inexpensive starting material, i.e. acetic anhydride, which is desirable from an economical point of view.

Since pure acetic anhydride is suitable in the process of this invention, highly concentrated aqueous solutions of acetic acid can be obtained after phase separation and work-up of the reaction mixture which can be recycled or used in other manufacturing processes. This leads to a reduced TOC (Total Organic Carbon) content in the production wastewater in comparison with the prior art processes which makes the process eco-friendly.

The process of this invention can be performed without any halogen-containing solvents and/or auxiliaries thus avoiding hazardous AOX compounds in the production wastewater, which is also desirable from an ecological point of view.

The process of this invention does not require a large excess of any of the reactants like hydrogen peroxide, acetic anhydride and bases in order to achieve high yields of the desired epoxide, which is desirable from both an economical and ecological point of view.

Furthermore, the process of this invention provides the desired epoxide, in particular terpinolene epoxide (IIa), in high yields.

The process provides a very good selectivity towards the epoxidation of the tetrasubsituted double bond in tetrasubstituted alkenes containing at least one (preferably one or two and more preferably one) additional carbon-carbon double bond (the additional carbon-carbon double bond preferably being disubstituted or trisubstituted, more preferably trisubstituted), e.g. terpinolene (Ia). For example, a very good chemoselective epoxidation of the exocyclic double bond in terpinolene (Ia) can be achieved. Thus, undesired side reactions leading to unwanted byproducts are minimized.

Accordingly, another subject matter of the present invention relates to the use of an oxidizing agent comprising hydrogen peroxide and acetic anhydride for the in-situ epoxidation of a tetrasubstituted alkene, preferably a tetrasubstituted alkene containing at least one (preferably one or two and more preferably one) additional carbon-carbon double bond (the additional carbon-carbon double bond preferably being disubstituted or trisubstituted, more preferably trisubstituted), e.g. terpinolene (Ia).

Yet another subject matter of the present invention relates to the use of an oxidizing agent comprising hydrogen peroxide and acetic anhydride for the selective in-situ epoxidation of a tetrasubstituted carbon-carbon double bond in a tetrasubstituted alkene, preferably a tetrasubstituted carbon-carbon double bond in a tetrasubstituted alkene containing at least one (preferably one or two and more preferably one) additional carbon-carbon double bond (the additional carbon-carbon double bond preferably being disubstituted or trisubstituted, more preferably trisubstituted) and in particular the exocyclic double bond in terpinolene (Ia).

The corresponding epoxide, in particular terpinolene epoxide (IIa), can also be easily isolated in high purity from the final reaction mixture by using conventional work-up procedures. The corresponding epoxide, in particular terpinolene epoxide (IIa), remains in the organic phase after phase separation whereas acetic acid, peroxo compounds such as unreacted peracetic acid and hydrogen peroxide and salts predominantly enter the aqueous phase which can be subjected to waste water treatment. Small amounts of acetic acid, peroxo compounds and salts still present in the organic phase can be removed by extractive work up and/or reduction of the peroxo compounds which contributes to a safely scalable process.

Any and all of these advantages make the process industrially simple, economical, safe and environmentally friendly.

Further embodiments of the invention are evident from the claims, the description and the examples. It is to be understood that the single features of the subject matter of the invention described herein can be applied not only in the combination given in each particular case but also in other combinations, without leaving the scope of the invention.

The starting materials according to the present invention are known compounds that are commercially available or can be prepared in a known manner.

The term “tetrasubstituted alkene” as used herein refers to an alkene having at least one carbon-carbon double bond wherein the carbon atoms of said double bond are bonded to a total of four carbon atoms excluding each other. The carbon-carbon double bond wherein the carbon atoms of said double bond are bonded to a total of four carbon atoms excluding each other is also referred to herein as “tetrasubstituted double bond”.

Examples of such tetrasubstituted alkenes include but are not limited to 2,3-dimethyl-2-butene, 2,3,4-trimethyl-2-pentene, terpinolene of the formula (Ia), 1,2-dimethylcyclohexene, 6-cadinene, and taxadiene.

Preferably, the tetrasubstituted alkene is selected from tetrasubstituted alkenes containing at least one (preferably one or two and more preferably one) additional carbon-carbon double bond.

More preferably, the tetrasubstituted alkene is selected from tetrasubstituted alkenes containing at least one additional carbon-carbon double bond, the additional carbon-carbon double bond being disubstituted or trisubstituted.

Even more preferably, the tetrasubstituted alkene is selected from tetrasubstituted alkenes containing at least one (preferably one or two and more preferably one) additional carbon-carbon double bond, the additional carbon-carbon double bond being trisubstituted.

In particular, the tetrasubstituted alkene is selected from tetrasubstituted alkenes containing one additional carbon-carbon double bond, the additional carbon-carbon double bond being trisubstituted.

In another embodiment,the tetrasubstitued alkene is selected from an alkene of the formula (I)

wherein R₁, R₂, R₃ and R₄ are different from hydrogen and independently of one another represent a substituent selected from the group consisting of C₁-C₆-alkyl, C₃-C₆-cycloalkyl, C₂-C₆-alkenyl, C₂-C₆-alkynyl and C₆-C₂₀-aryl, or R₁ and R₂, or R₁ and R₃, or R₂ and R₄, or R₃ and R₄ in each case together represent a C₂-C₁₀-alkylene or C₂-C₁₀-alkenylene chain and form a 3-, 4-, 5-, 6-, 7-, 8-, 9-, 10-, 11- or 12-membered saturated or partially unsaturated monocyclic ring together with the one or two carbon atoms they are bonded to, wherein any one of the aforementioned substituents or C₂-C₁₀-alkylene or C₂-C₁₀-alkenylene chains may be substituted by one or more substituents each independently selected from the group consisting of halogen, C₁-C₆-alkyl and C₁-C₆-haloalkyl.

The organic moieties mentioned in the definition of the variables R¹, R², R³ and R⁴ are—like the term halogen—collective terms for individual enumerations of the individual group members. The term “halogen” denotes in each case fluorine, chlorine, bromine or iodine. All hydrocarbon chains, e.g. alkyl or alkenyl chains, can be straight-chain or branched, the prefix C_(n)-C_(m) denoting in each case the possible number of carbon atoms in the group.

Examples of such meanings are:

-   -   C₁-C₆-alkyl: for example CH₃, C₂H₅, n-propyl, CH(CH₃)₂, n-butyl,         CH(CH₃)—C₂H₅, CH₂—CH(CH₃)₂, C(CH₃)₃, n-pentyl, 1-methylbutyl,         2-methylbutyl, 3-methylbutyl, 2,2-dimethylpropyl, 1-ethylpropyl,         n-hexyl, 1,1-dimethylpropyl, 1,2-dimethylpropyl, 1-methylpentyl,         2-methylpentyl, 3-methylpentyl, 4-methylpentyl,         1,1-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl,         2,2-dimethylbutyl, 2,3-dimethylbutyl, 3,3-dimethylbutyl,         1-ethylbutyl, 2-ethylbutyl, 1,1,2-trimethylpropyl,         1,2,2-trimethylpropyl, 1-ethyl-1-methylpropyl or         1-ethyl-2-methylpropyl, preferably methyl, ethyl, n-propyl,         1-methylethyl, n-butyl, 1,1-dimethylethyl, n-pentyl or n-hexyl;     -   C₃-C₆-cycloalkyl: for example cyclopropyl, cyclobutyl,         cyclopentyl and cyclohexyl;     -   C₂-C₆-alkenyl, for example, ethenyl, 1-propenyl, 2-propenyl,         1-methylethenyl 1-butenyl, 2-butenyl, 3-butenyl,         1-methyl-1-propenyl, 2-methyl-1-propenyl, 1-methyl-2-propenyl,         2-methyl-2-propenyl, 1-pentenyl, 2-pentenyl, 3-pentenyl,         4-pentenyl, 1-methyl-1-butenyl, 2-methyl-1-butenyl,         3-methyl-1-butenyl, 1-methyl-2-butenyl, 2-methyl-2-butenyl,         3-methyl-2-butenyl, 1-methyl-3-butenyl, 2-methyl-3-butenyl,         3-methyl-3-butenyl, 1,1-dimethyl-2-propenyl,         1,2-dimethyl-1-propenyl, 1,2-dimethyl-2-propenyl,         1-ethyl-1-propenyl, 1-ethyl-2-propenyl, 1-hexenyl, 2-hexenyl,         3-hexenyl, 4-hexenyl, 5-hexenyl, 1-methyl-1-pentenyl,         2-methyl-1-pentenyl, 3-methyl-1-pentenyl, 4-methyl-1-pentenyl,         1-methyl-2-pentenyl, 2-methyl-2-pentenyl, 3-methyl-2-pentenyl,         4-methyl-2-pentenyl, 1-methyl-3-pentenyl, 2-methyl-3-pentenyl,         3-methyl-3-pentenyl, 4-methyl-3-pentenyl, 1-methyl-4-pentenyl,         2-methyl-4-pentenyl, 3-methyl-4-pentenyl, 4-methyl-4-pentenyl,         1,1-dimethyl-2-butenyl, 1,1-dimethyl-3-butenyl,         1,2-dimethyl-1-butenyl, 1,2-dimethyl-2-butenyl,         1,2-dimethyl-3-butenyl, 1,3-dimethyl-1-butenyl,         1,3-dimethyl-2-butenyl, 1,3-dimethyl-3-butenyl,         2,2-dimethyl-3-butenyl, 2,3-dimethyl-1-butenyl,         2,3-dimethyl-2-butenyl, 2,3-dimethyl-3-butenyl,         3,3-dimethyl-1-butenyl, 3,3-dimethyl-2-butenyl,         1-ethyl-1-butenyl, 1-ethyl-2-butenyl, 1-ethyl-3-butenyl,         2-ethyl-1-butenyl, 2-ethyl-2-butenyl, 2-ethyl-3-butenyl,         1,1,2-trimethyl-2-propenyl, 1-ethyl-1-methyl-2-propenyl,         1-ethyl-2-methyl-1-propenyl or 1-ethyl-2-methyl-2-propenyl;     -   C₂-C₆-alkynyl: for example ethynyl, 1-propynyl, 2-propynyl,         1-butynyl, 2-butynyl, 3-butynyl, 1-methyl-2-propynyl,         1-pentynyl, 2-pentynyl, 3-pentynyl, 4-pentynyl,         1-methyl-2-butynyl, 1-methyl-3-butynyl, 2-methyl-3-butynyl,         3-methyl-1-butynyl, 1,1-dimethyl-2-propynyl, 1-ethyl-2-propynyl,         1-hexynyl, 2-hexynyl, 3-hexynyl, 4-hexynyl, 5-hexynyl,         1-methyl-2-pentynyl, 1-methyl-3-pentynyl, 1-methyl-4-pentynyl,         2-methyl-3-pentynyl, 2-methyl-4-pentynyl, 3-methyl-1-pentynyl,         3-methyl-4-pentynyl, 4-methyl-1-pentynyl, 4-methyl-2-pentynyl,         1,1-dimethyl-2-butynyl, 1,1-dimethyl-3-butynyl,         1,2-dimethyl-3-butynyl, 2,2-dimethyl-3-butynyl,         3,3-dimethyl-1-butynyl, 1-ethyl-2-butynyl, 1-ethyl-3-butynyl,         2-ethyl-3-butynyl or 1-ethyl-1-methyl-2-propynyl;     -   C₂-C₁₀-alkylene: a straight carbon chain having from 2 to 10         carbon atoms and having only carbon-carbon single bonds, for         example ethylene (CH₂CH₂), n-propylene (CH₂CH₂CH₂), n-butylene         (CH₂CH₂CH₂CH₂), n-pentylene (CH₂CH₂CH₂CH₂CH₂), n-hexylene         (—(CH₂)₆—), n-heptylene (—(CH₂)₇—), n-octylene (—(CH₂)₈—),         n-nonylene (—(CH₂)₉—) and n-decylene (—(CH₂)₁₀—);     -   C₂-C₁₀-alkenylene chain: a straight carbon chain having from 2         to 10 carbon atoms and at least one carbon-carbon double bond         and no carbon-carbon triple bond, for example, CH═CH, CH═CH—CH₂,         CH═CH—CH₂CH₂, CH═CH—CH═CH₂ and CH═CH—CH₂CH₂CH₂;     -   C₁-C₆-haloalkyl: a C₁-C₆-alkyl radical as mentioned above which         is partially or fully substituted by fluorine, chlorine, bromine         and/or iodine, i.e., for example, chloromethyl, dichloromethyl,         trichloromethyl, fluoromethyl, difluoromethyl, trifluoromethyl,         chlorofluoromethyl, dichlorofluoromethyl, chlorodifluoromethyl,         bromomethyl, iodomethyl, 2-fluoroethyl, 2-chloroethyl,         2-bromoethyl, 2-iodoethyl, 2,2-difluoroethyl,         2,2,2-trifluoroethyl, 2-chloro-2-fluoroethyl,         2-chloro-2,2-difluoroethyl, 2,2-dichloro-2-fluoroethyl,         2,2,2-trichloroethyl, pentafluoroethyl, 2-fluoropropyl,         3-fluoropropyl, 2,2-difluoropropyl, 2,3-difluoropropyl,         2-chloropropyl, 3-chloropropyl, 2,3-dichloropropyl,         2-bromopropyl, 3-bromopropyl, 3,3,3-trifluoropropyl,         3,3,3-trichloropropyl, 2,2,3,3,3-pentafluoropropyl,         heptafluoropropyl, 1-(fluoromethyl)-2-fluoroethyl,         1-(chloromethyl)-2-chloroethyl, 1-(bromomethyl)-2-bromoethyl,         4-fluorobutyl, 4-chlorobutyl, 4-bromobutyl, nonafluorobutyl,         5-fluoropentyl, 5-chloropentyl, 5-bromopentyl, 5-iodopentyl,         undecafluoropentyl, 6-fluorohexyl, 6-chlorohexyl, 6-bromohexyl,         6-iodohexyl or dodecafluorohexyl.

The term “C₆-C₂₀-aryl” refers to an unsaturated aromatic carbocyclic group of from 6 to 20 carbon atoms having a single ring (e.g., phenyl) or multiple condensed (fused) rings, wherein at least one ring is aromatic (e.g. naphthalenyl or dihydrophenanthrenyl). Examples of C₆-C₂₀-aryls include phenyl, naphthalenyl, anthracenyl, indenyl or phenanthrenyl. A preferred aryl group is phenyl.

In another embodiment, the tetrasubstituted alkene is selected from terpenes, preferably cyclic terpenes, more preferably p-menthadienes and even more preferably terpinolene (Ia).

The term “terpenes” as used herein refers to natural substances constructed from isoprene basic units and derivatives. Depending on the number of basic units, terpene units are classified as monoterpenes, sesquiterpenes, diterpenes, sesterpenes, triterpenes, and tetraterpenes.

In another embodiment, the tetrasubstituted alkene is selected from cyclic terpenes comprising at least one (preferably one) exocyclic or endocyclic double bond, in particular at least one (preferably one) tetrasubstituted exocyclic or endocyclic double bond.

In another embodiment, the tetrasubstituted alkene is selected from cyclic terpenes comprising at least one (preferably one) exocyclic double bond, in particular at least one (preferably one) tetrasubstituted exocyclic double bond.

In another embodiment, the tetrasubstituted alkene is selected from cyclic terpenes comprising at least one (preferably one) endocyclic double bond, in particular at least one (preferably one) tetrasubstituted endocyclic double bond.

In another embodiment, the tetrasubstituted alkene is selected from cyclic terpenes comprising at least one (preferably one) exocyclic double bond, in particular at least one (preferably one) tetrasubstituted exocyclic double bond, and at least one (preferably one) endocyclic double bond, in particular at least one (preferably one) di- or trisubstituted (preferably trisubstituted) endocyclic double bond.

The term “exocyclic double bond” as used herein refers to a double bond between two carbon atoms wherein at least one carbon atom of the double bond is not constituent of the carbocyclic ring system. In one embodiment, the term “exocyclic double bond” refers to a double bond between two carbon atoms wherein one carbon atom of the double bond is not constituent of the carbocyclic ring system, while the other carbon atom of the double bond is constituent of the carbocyclic ring system. In another embodiment, the term “exocyclic double bond” refers to a double bond between two carbon atoms wherein both carbon atoms of the double bond are not constituent of the carbocyclic ring system.

The term “endocyclic double bond” as used herein refers to a double bond between two carbon atoms wherein both carbon atoms of the double bond are constituent of the carbocyclic ring system.

The terms “exocyclic double bond” and “endocyclic double bond” are further illustrated by the following scheme:

Most preferably, the tetrasubstituted alkene is terpinolene of the formula (Ia)

In another embodiment of this invention, the tetrasubstituted alkene is terpinolene of the formula (Ia) and the corresponding epoxide is terpinolene epoxide of formula (IIa)

Thus, a particularly preferred embodiment of this invention relates to a process for the epoxidation of terpinolene of the formula (Ia) to terpinolene epoxide of formula (IIa) comprising reacting the terpinolene of the formula (Ia) with peracetic acid prepared in situ from acetic anhydride and hydrogen peroxide in the presence of at least one buffering agent.

Other names of terpinolene (Ia) include p-Mentha-1,4(8)-diene, 1-Methyl-4-(1-methylethylidene)cyclohexene or 4-Isopropylidene-1-methylcyclohexene. Terpinolene used to be manufactured by fractional distillation of wood turpentine. It is now produced by treating alpha-pinene with aqueous phosphoric acid at 75° C. (see Eggersdorfer, M.; Terpenes. Ullmann's Encyclopedia of Industrial Chemistry. Vol. 36, 2012, Wiley-VCH Verlag, Weinheim).

The epoxidation of the tetrasubstituted alkene according to the present invention is carried out by reacting the tetrasubstituted alkene with peracetic acid prepared in situ from acetic anhydride and hydrogen peroxide.

Acetic anhydride is preferably used as the pure material.

Hydrogen peroxide can be used herein in all commercially available forms, for example, in the form of aqueous hydrogen peroxide solutions, as pure hydrogen peroxide, anhydrous hydrogen peroxide dissolved in organic solvents or in the form of compounds which are capable of releasing hydrogen peroxide under the reaction conditions (e.g. metal peroxides such as magnesium peroxide or zinc peroxide) as well as hydrogen peroxide adducts, such as, for example, urea hydrogen peroxide (also abbreviated as “UHP”). The most common form of urea hydrogen peroxide is the 1:1 molar adduct of urea and hydrogen peroxide (CO(NH₂)₂.H₂O₂).

In a preferred embodiment, hydrogen peroxide is used as an aqueous solution, whereby the concentration of the solution is not critical. Preferably, the aqueous solution of hydrogen peroxide comprises at least 30% by weight and more preferably at least 50% by weight of hydrogen peroxide. Usually, the aqueous solution of hydrogen peroxide comprises 10% to 70% by weight, preferably 30 to 50% by weight of hydrogen peroxide.

In another embodiment, the presence of urea hydrogen peroxide is excluded.

In another embodiment of the use of this invention, the oxidizing agent excludes the presence of urea hydrogen peroxide.

In another embodiment of the use of this invention, the oxidizing agent comprises a combination of an aqueous solution of hydrogen peroxide and acetic anhydride.

In another embodiment of the use of this invention, the oxidizing agent comprises a combination of an aqueous solution of hydrogen peroxide and acetic anhydride, said oxidizing agent excluding the presence of urea hydrogen peroxide.

The molar ratio of acetic anhydride to the tetrasubstituted alkene, in particular terpinolene (Ia), can vary widely and depends on the reaction conditions used, but is generally from 0.8:1 to 2:1, preferably from 0.9:1 to 1.8:1, more preferably from 1:1 to 1.6:1 and even more preferably from 1:1 to 1.4:1.

The molar ratio of hydrogen peroxide to the tetrasubstituted alkene, in particular terpinolene (Ia), can likewise vary widely and depends on the reaction conditions used, but is generally from 1.1:1 to 1.9:1, preferably from 1.1:1 to 1.8:1, more preferably from 1.2:1 to 1.6:1 and even more preferably from 1.2:1 to 1.4:1.

Advantageously, no excess amounts or only slight excess amounts of hydrogen peroxide relative to acetic anhydride are required to conduct the epoxidation reaction according to the invention. Preferably, the molar ratio of hydrogen peroxide to acetic anhydride is from 2.0:1.9 to 1.1:1.05, more preferably from 1.8:1.7 to 1.15:1.1, even more preferably from 1.6:1.5 to 1.2:1.15 and in particular from 1.4:1.3 to 1.25:1.2.

The epoxidation of the tetrasubstituted alkene according to the present invention is carried out in the presence of at least one buffering agent.

It is preferable that the pH of the reaction mixture is maintained within a range of 2 to 5, more preferably within a range of 3 to 4.

Thus, in a preferred embodiment, the buffering agent is capable of maintaining the pH of the reaction mixture within a range of 2 to 5, more preferably within a range of 3 to 4.

In another preferred embodiment, the buffering agent is present in an amount sufficient to maintain the pH of the reaction mixture within a range of 2 to 5, more preferably within a range of 3 to 4.

The molar ratio of buffering agent to the tetrasubstituted alkene, in particular terpinolene (Ia), can vary and depends on the nature of the buffering agent and the reaction conditions used, but is generally from 0.1:1 to 0.9:1, preferably from 0.1:1 to 0.8:1, more preferably from 0.1:1 to 0.6:1 and even more preferably from 0.2:1 to 0.4:1.

Preferably, the buffering agent is selected from salts of inorganic acids, salts of organic acids and any combination thereof, more preferably selected from alkali metal and alkaline earth metal salts of inorganic acids, organic acids and any combination thereof.

The term “alkali metal” as used herein includes but is not limited to lithium, sodium and potassium.

The term “alkaline earth metal” as used herein includes but is not limited to calcium and magnesium.

More preferably, the buffering agent is a salt selected from phosphates, formates, acetates, carbonates, citrates, sulfates, cacodylates, fumarates, malates, tartrates and any combination thereof, even more preferably selected from phosphates, formates, acetates, carbonates, citrates, sulfates and any combination thereof, yet more preferably selected from phosphates, acetates, carbonates and any combination thereof, still more preferably selected from phosphates, acetates and any combination thereof and in particular selected from acetates. In another embodiment, the buffering agent is a salt selected from phosphates.

The term “phosphates” as used herein refers to salts comprising a phosphate ion (PO₄ ³⁻), a hydrogen phosphate ion (HPO₄ ²⁻), a dihydrogen phosphate ion (H₂PO₄ ⁻), a diphosphate ion (P₂O₇ ⁴⁻), a hydrogen diphosphate ion (HP₂O₇ ³⁻), a dihydrogen diphosphate ion (H₂P₂O₇ ²⁻), a polyphosphate ion (P_(n)O_(3n+1) ^((n+2)−), wherein n is an integer greater than or equal to 3) such as, for example, a triphosphate ion (P₃O₁₀ ⁵⁻) or a tetraphosphate ion (P₄O₁₄ ⁶⁻), or a cyclic metaphosphate ion ((PO₃ ⁻)_(n) wherein n is an integer greater than or equal to 3) such as, for example, a cyclic trimetaphosphate ion P₃O₉ ³⁻.

The term “formates” as used herein refers to salts derived from formic acid, i.e. salts comprising the formate or methanoate ion (HCOO⁻).

The term “acetates” as used herein refers to salts derived from acetic acid, i.e. salts comprising the acetate or ethanoate ion (CH₃COO⁻).

The term “carbonates” as used herein refers to salts comprising the carbonate ion (CO₃ ²⁻) or hydrogen carbonate ion (HCO₃ ⁻).

The term “citrates” as used herein refers to salts derived from citric acid, i.e. salts comprising the citrate ion (C₃H₅O(CO)₃ ³⁻).

The term “cacodylates” as used herein refers to salts derived from cacodylic acid, i.e. salts comprising the cacodylate ion ((CH₃)₂AsO²⁻).

The term “fumarates” as used herein refers to salts derived from fumaric acid, i.e. salts comprising the fumarate dianion (—OOC—CH═CH—COO⁻).

The term “malates” as used herein refers to salts derived from malic acid, i.e. salts comprising the malate dianion (⁻OOC—CH₂—CH(OH)—COO⁻).

The term “tartrates” as used herein refers to salts derived from tartaric acid, i.e. salts comprising the tartrate dianion (⁻OOC—CH(OH)—CH(OH)—COO⁻).

The term “sulfates” as used herein refers to salts derived from sulfuric acid, i.e. salts comprising the sulfate ion (SO₄ ²⁻).

More preferably, the buffering agent is selected from alkali metal and alkaline earth metal phosphates, alkali metal and alkaline earth metal formates, alkali metal and alkaline earth metal acetates, alkali metal and alkaline earth metal carbonates, alkali metal and alkaline earth metal citrates, alkali metal and alkaline earth metal sulfates and any combination thereof, even more preferably selected from alkali metal and alkaline earth metal phosphates, alkali metal and alkaline earth metal formates, alkali metal and alkaline earth metal acetates, alkali metal and alkaline earth metal carbonates, alkali metal and alkaline earth metal citrates and any combination thereof, yet more preferably selected from alkali metal and alkaline earth metal phosphates, alkali metal and alkaline earth metal acetates, alkali metal and alkaline earth metal carbonates and any combination thereof, in particular selected from alkali metal and alkaline earth metal phosphates, alkali metal and alkaline earth metal acetates and any combination thereof and most preferably selected from alkali metal and alkaline earth metal acetates. In another embodiment, the buffering agent is selected from alkali metal and alkaline earth metal phosphates.

In another embodiment, the buffering agent is selected from di-(alkali metal) hydrogen phosphates, alkali metal dihydrogen phosphates, alkali metal formates, alkali metal acetates, alkali metal hydrogen carbonates, alkali metal citrates, alkali metal sulfates and any combination thereof, preferably from di-(alkali metal) hydrogen phosphates, alkali metal acetates, alkali metal hydrogen carbonates, alkaline earth metal carbonates and any combination thereof and more preferably from di-(alkali metal) hydrogen phosphates, alkali metal acetates and any combination thereof. Most preferably, the buffering agent is selected from alkali metal acetates. In another embodiment, the buffering agent is selected from di-(alkali metal) hydrogen phosphates.

In another embodiment, the buffering agent is selected from lithium phosphate, sodium phosphate, potassium phosphate, calcium phosphate, magnesium phosphate, dilithium hydrogen phosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, calcium hydrogen phosphate, magnesium hydrogen phosphate, lithium dihydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, calcium dihydrogen phosphate, magnesium dihydrogen phosphate, lithium formate, sodium formate, potassium formate, calcium formate, magnesium formate, lithium acetate, sodium acetate, potassium acetate, calcium acetate, magnesium acetate, lithium carbonate, sodium carbonate, potassium carbonate, calcium carbonate, magnesium carbonate, lithium hydrogen carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, calcium hydrogen carbonate, magnesium hydrogen carbonate, lithium citrate, sodium citrate, potassium citrate, calcium citrate, magnesium citrate, lithium sulfate, sodium sulfate, potassium sulfate, calcium sulfate, magnesium sulfate and any combination thereof.

More preferably, the buffering agent is selected from disodium hydrogen phosphate, dipotassium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, sodium formate, potassium formate, lithium acetate, sodium acetate, potassium acetate, calcium acetate, magnesium acetate, calcium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium citrate, potassium citrate, lithium sulfate, sodium sulfate, potassium sulfate, calcium sulfate, magnesium sulfate and any combination thereof.

Even more preferably, the buffering agent is selected from disodium hydrogen phosphate, dipotassium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, lithium acetate, sodium acetate, potassium acetate, calcium acetate, magnesium acetate, sodium hydrogen carbonate, potassium hydrogen carbonate, calcium carbonate and any combination thereof.

Yet more preferably, the buffering agent is selected from disodium hydrogen phosphate, dipotassium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate, lithium acetate, sodium acetate, potassium acetate, calcium acetate, magnesium acetate and any combination thereof.

In particular, the buffering agent is selected from lithium acetate, sodium acetate, potassium acetate, calcium acetate, magnesium acetate and any combination thereof. Most preferably, the buffering agent is sodium acetate, potassium acetate or a combination thereof.

In another embodiment, the buffering agent is selected from disodium hydrogen phosphate, dipotassium hydrogen phosphate, sodium dihydrogen phosphate, potassium dihydrogen phosphate and any combination thereof.

In a preferred embodiment, the process of this invention is carried out in the presence of at least one inert organic solvent. By “inert organic solvent” is meant an organic solvent which, under the reaction conditions of the process of this invention, does not enter into any appreciable reaction with either the reactants or the products.

In another embodiment, the process of this invention is carried out in the absence of at least one inert organic solvent.

In another embodiment, the inert organic solvent is selected from non-halogenated inert organic solvents.

The inert organic solvent used in the process of this invention is preferably selected from non-halogenated aliphatic hydrocarbons, non-halogenated cycloaliphatic hydrocarbons, non-halogenated aromatic hydrocarbons, halogenated aliphatic hydrocarbons, halogenated aromatic hydrocarbons, amides, ethers, esters, ketones, nitriles and any combination thereof. Examples of suitable non-halogenated aliphatic hydrocarbons include pentane, hexane, heptane, and the like. Preference is given to saturated aliphatic hydrocarbons having from 5 to 10 carbon atoms.

Examples of suitable non-halogenated cycloaliphatic hydrocarbons include cyclopentane, cyclohexane, cycloheptane, and the like. Preference is given to non-halogenated saturated cycloaliphatic hydrocarbons having from 5 to 10 carbon atoms. Cyclohexane is particularly preferred.

Examples of suitable a non-halogenated aromatic hydrocarbons include toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, 2-propylbenzene (cumene), 2-isopropyltoluene (o-cymol), 3-isopropyltoluene (m-cymol), 4-isopropyltoluene (p-cymol), 1,3,5-trimethylbenzene (mesitylene), and the like. Preference is given to toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, 1,3,5-trimethylbenzene (mesitylene), and any combination thereof. Especially preferred among the non-halogenated aromatic hydrocarbons are toluene, o-xylene, m-xylene, p-xylene, and any combination thereof, with toluene being the most preferred.

Examples of suitable halogenated aliphatic hydrocarbons include methylene chloride, chloroform, carbon tetrachloride, 1,2-dichloroethane, 1,1,1,2-tetrachloroethane, 1,1,2,2-tetrachloroethane, 1,1-dichloroethylene, 1,2-dichloroethylene, and the like. Preference is given to methylene chloride and 1,2-dichloroethane and any combination thereof.

Examples of suitable halogenated aromatic hydrocarbons include chlorobenzene, bromobenzene, o-dichlorobenzene, m-dichlorobenzene, α,α,α-trifluorotoluene (benzotrifluoride) and the like.

Examples of suitable amides include N,N-dimethylformamide, dimethylacetamide, diethylacetamide, and the like.

Examples of suitable ethers include cyclic and acyclic ethers such as diethyl ether, diisopropyl ether, n-butyl methyl ether, isobutyl methyl ether, sec-butyl methyl ether, tert-butyl methyl ether, cyclopentyl methyl ether, tetrahydrofuran, 1,4-dioxane, and the like.

Examples of suitable esters include ethyl acetate, n-propylacetate, isopropyl acetate, tert-butyl acetate, and the like.

Examples of suitable ketones include acetone, methyl ethyl ketone, methyl isopropyl ketone, methyl isobutyl ketone, cyclopropyl methyl ketone and the like.

Examples of suitable nitriles include acetonitrile, benzonitrile, and the like.

In a preferred embodiment, the inert organic solvent is selected from non-halogenated aliphatic hydrocarbons, non-halogenated cycloaliphatic hydrocarbons, non-halogenated aromatic hydrocarbons, halogenated aliphatic hydrocarbons and any combination thereof.

In a more preferred preferred embodiment, the inert organic solvent is selected from heptane, cyclohexane, cycloheptane, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, 1,3,5-trimethylbenzene (mesitylene), methylene chloride and any combination thereof.

In an even more preferred embodiment, the inert organic solvent is selected from heptane, cyclohexane, toluene, methylene chloride and any combination thereof.

In another embodiment, the inert organic solvent is selected from non-halogenated hydrocarbons, preferably from non-halogenated aliphatic hydrocarbons, non-halogenated cycloaliphatic hydrocarbons, non-halogenated aromatic hydrocarbons and any combination thereof, more preferably from heptane, cyclohexane, cycloheptane, toluene, o-xylene, m-xylene, p-xylene, ethylbenzene, 1,3,5-trimethylbenzene (mesitylene) and any combination thereof.

Still more preferably, the inert organic solvent is selected from heptane, cyclohexane, toluene and any combination thereof.

Particularly preferred inert organic solvents are non-halogenated aromatic hydrocarbons, especially non-halogenated alkylbenzenes which are mono-, di-, or trialkylsubstituted with each alkyl group containing 1 to 3 carbon atoms, and in particular those selected from the group consisting of toluene, o-xylene, m-xylene, p-xylene, and any combination thereof. Most preferably, the inert organic solvent is toluene.

The volume ratio of the inert organic solvent to the tetrasubstituted alkene, in particular terpinolene (Ia), is generally from 0.01:1 to 20:1, preferably from 0.1:1 to 15:1, more preferably from 0.5:1 to 10:1, and most preferably from 1:1 to 5:1.

The process of the present invention can be carried out under atmospheric pressure or under slightly elevated or reduced pressure. Typically, the atmospheric pressure is employed.

The temperature used in the process of the present invention can vary widely and is preferably from 0 to 50° C., more preferably from 0 to 40° C. and even more preferably from 10 to 40° C.

The reaction time can vary in a wide range and depends on a variety of factors such as, for example, temperature, pressure, or the reagents and auxiliary substances used. Typical reaction times are in the range of from 1 to 20 hours, preferably from 2 to 15 hours and more preferably from 3 to 10 hours.

In a preferred embodiment, the reaction of the tetrasubstituted alkene (in particular terpinolene (Ia)) with peracetic acid prepared in situ from acetic anhydride and hydrogen peroxide comprises the steps of

-   -   (a) Providing a first mixture comprising the tetrasubstituted         alkene (in particular terpinolene (Ia)), acetic anhydride, the         buffering agent and optionally the inert organic solvent,     -   (b) Adding hydrogen peroxide to the first mixture under         agitation to form a second mixture, and     -   (c) Agitating the second mixture.

In another embodiment, step (a) is carried out by following the steps of

-   -   (a1) Providing a mixture comprising the tetrasubstituted alkene         (in particular terpinolene (Ia)), the buffering agent and         optionally the inert organic solvent, and     -   (a2) adding acetic anhydride to the mixture obtained from step         (a1) to give the first mixture.

Step (a) is preferably carried out at a temperature of 0 to 50° C., more preferably 10 to 30° C.

In step (b), hydrogen peroxide is preferably added under agitation to the first mixture at a temperature of 0 to 50° C., more preferably 10 to 50° C. and even more preferably 10 to 40° C.

In step (b), hydrogen peroxide is preferably added under agitation to the first mixture over a period of at least 10 minutes, more preferably at least 1 hour, even more preferably at least 3 hours and in particular from 3 to 8 hours.

Preferably, hydrogen peroxide is added under agitation to the first mixture at a temperature of at least 20° C., more preferably at least 30° C. and in particular 30 to 50° C. over a period of at least 3 hours (in particular 3 to 8 hours). Any and all these measures are predominantly intended to prevent accumulation of the explosive peracetic acid in the reaction mixture.

In another embodiment, a stabilizing agent can be employed in the peroxy-containing reaction mixture. Such stabilizers are well known and are, for example, urea, pyridine N-oxide, 2,3-pyridine-dicarboxylic acid, 2,6-pyridinedicarboxylic acid, phosphates, diphosphates, polyphosphates, metaphosphates, ethylenediaminetetraacetic acid (EDTA) and any combination thereof. The stabilizing agent should be present in the reaction mixture in an amount of 0.1 to 10% by weight of the reaction mixture.

In another embodiment, an organic radical scavenger may be present in the reaction mixture. Non limiting examples of organic radical scavengers include phenols such as, for example, hydroquinone, monomethylhydroquinone, 2,6-Bis(1,1-dimethylethyl)-4-methylphenol (BHT) and any combination thereof. The organic radical scavenger may be used in an amount of 0.01 to 10% by weight of the reaction mixture.

Step (c) is preferably carried out at a temperature of 0 to 40° C., more preferably 10 to 40° C.

The corresponding epoxide (in particular terpinolene epoxide (IIa)) is preferably isolated from the final reaction mixture obtained in step (c) by employing conventional methods, for example by extraction, in particular extraction with a basic or neutral aqueous medium, distillation, and the like.

In another embodiment, excess peroxo compounds present in the final reaction mixture are reduced before or after work up of the reaction mixture. The term “excess peroxo compounds” as used herein includes unreacted peracetic acid and/or unreacted hydrogen peroxide still present in the final reaction mixture obtained after completion or partial completion of the reaction. Preferably, the final reaction mixture or the organic phase separated from the final reaction mixture is treated with at least one reducing agent. Any suitable reducing agent may be employed in carrying out process of this invention, however, it is preferred to employ a reducing agent selected from alkali metal sulfites, alkaline earth metal sulfites, sulfur dioxide, formaldehyde, paraformaldehyde, iron (III) salts (such as, for example, iron (III) chloride, iron (III) sulfate or iron (III) acetate), manganese dioxide, catalase and any combination thereof, more preferably from alkali metal sulfites, in particular sodium sulfite (Na₂SO₃), potassium sulfite (K₂SO₃) or a combination thereof. The reducing agent may be used in pure form or as an aqueous solution, preferably as an aqueous solution. For example, an aqueous solution comprising 10 to 30% by weight of an alkali metal sulfite, in particular sodium sulfite (Na₂SO₃), potassium sulfite (K₂SO₃) or a combination thereof is employed as the reducing agent.

In another embodiment, the process of this invention further comprises separating the final reaction mixture into an aqueous phase and an organic phase and removing excess amounts of acetic acid, peracetic acid and hydrogen peroxide from the organic phase by aqueous extraction, in particular with water or with an aqueous base solution. Suitable bases employed in the aqueous base solution include but are not limited to alkali metal and alkaline earth metal hydroxides, alkali metal and alkaline earth metal carbonates, alkali metal and alkaline earth metal hydrogen carbonates or any combination thereof, preferably alkali metal hydroxides, in particular sodium hydroxide, potassium hydroxide or a combination thereof. For example, an aqueous solution comprising 1 to 20% by weight of an alkali metal hydroxide, in particular sodium hydroxide, potassium hydroxide or a combination thereof is employed for the aqueous extraction.

In another embodiment, the final reaction mixture is distilled to obtain the corresponding epoxide (in particular terpinolene epoxide (IIa)), optionally the inert solvent and a residue. Further, the organic phase obtained from phase separation of the final reaction mixture can also be subjected to distillation.

In another embodiment, the tetrasubstituted alkene (in particular terpinolene (Ia)) is partially converted to the corresponding epoxide (in particular terpinolene epoxide (IIa)) and recycled, preferably to step (a) or more specifically to step (a1). Such partial conversion is particularly advantageous for increasing the selectivity towards the epoxidation of the tetrasubsituted double bond in tetrasubstituted alkenes containing at least one additional carbon-carbon double bond (in particular an additional trisubstituted double bond), e.g. terpinolene (Ia). For this purpose, the tetrasubstituted alkene (in particular terpinolene (Ia) is isolated from the reaction mixture after partial completion of the reaction by using any or all the aforementioned work-up procedures in an analogous manner, in particular phase separation, aqueous extraction of the organic phase, reductive treatment of the reaction mixture obtained after partial completion of the reaction or of the organic phase obtained from phase separation in order to remove excess amounts of peroxo compounds and distillation of the reaction mixture obtained after partial completion of the reaction or of the organic phase obtained from phase separation to separate the corresponding epoxide (in particular terpinolene epoxide (IIa), unreacted tetrasubstituted alkene (in particular unreacted terpinolene (Ia)) and by-products. The fraction of the unreacted tetrasubstituted alkene (in particular unreacted terpinolene (Ia)) can be recycled to a new epoxidation reaction, and the fraction of the corresponding epoxide (in particular terpinolene epoxide (IIa)) can be forwarded to a subsequent reaction step.

In another embodiment, terpinolene epoxide of formula (IIa) is further converted to limonene-4-ol.

In another embodiment, terpinolene epoxide of formula (IIa) is further converted to terpinene-4-ol.

Preferably, terpinolene epoxide of formula (IIa) is further converted via limonene-4-ol to terpinene-4-ol.

For example, terpinolene epoxide of formula (IIa) can be further subjected to an epoxide ring opening isomerization leading to limonene-4-ol, optionally followed by conventional hydrogenation to give terpinene-4-ol, as described, for example in GB 1 307 053.

Terpinene-4-ol can in turn be used as a starting material for the synthesis of oxabicycloalkane herbicides, in particular of (±)-2-exo-(2-Methylbenzyloxy)-1-methyl-4-isopropyl-7-oxabicyclo[2.2.1]heptane as described, for example in U.S. Pat. No. 4,487,945 or U.S. Pat. No. 4,542,244.

(±)-2-exo-(2-Methylbenzyloxy)-1-methyl-4-isopropyl-7-oxabicyclo[2.2.1]heptane (herein also referred to as the “exo-(±)-isomers”, CAS RN 87818-31-3)

is the racemic mixture containing equal parts of the two enantiomers (+)-2-exo-(2-Methylbenzyloxy)-1-methyl-4-isopropyl-7-oxabicyclo[2.2.1]heptane (herein also referred to as the “exo-(+)-isomer”, CAS RN 87818-61-9) and (−)-2-exo-(2-Methylbenzyloxy)-1-methyl-4-isopropyl-7-oxabicyclo[2.2.1]heptane (herein also referred to as the “exo-(−)-isomer”, CAS RN 87819-60-1). The exo-(±)-isomers, the exo-(+)-isomer and the exo-(−)-isomer including their preparation and herbicidal properties are disclosed in EP 0 081 893 A2 (see Examples 29, 34, 35 and 62). Further preparation methods of these compounds are described in U.S. Pat. No. 4,487,945 (see Embodiments 46 and 48). The racemic mixture (±)-2-exo-(2-Methylbenzyloxy)-1-methyl-4-isopropyl-7-oxabicyclo[2.2.1]heptane is also described in the The Pesticide Manual, Fourteenth Edition, Editor: C. D. S. Tomlin, British Crop Production Council, 2006, entry 157, pages 195-196 with its common name cinmethylin, its IUPAC name (1RS,2SR,4SR)-1,4-epoxy-p-menth-2-yl 2-methylbenzyl ether and its Chemical Abstracts name exo-(±)-1-methyl-4-(1-methylethyl)-2-[(2-methylphenyl)methoxy]-7-oxabicyclo[2.2.1]heptane.

Any of terpinolene epoxide of formula (IIa), limonene-4-ol and terpinene-4-ol are valuable intermediates in the preparation of (±)-2-exo-(2-Methylbenzyloxy)-1-methyl-4-isopropyl-7-oxabicyclo[2.2.1]heptane, any of its individual enantiomers or any non-racemic mixture thereof.

Any of terpinolene epoxide of formula (IIa), limonene-4-ol and terpinene-4-ol may be further converted into (±)-2-exo-(2-Methylbenzyloxy)-1-methyl-4-isopropyl-7-oxabicyclo[2.2.1]heptane, any of its individual enantiomers or any non-racemic mixture thereof. Further conversion into (±)-2-exo-(2-Methylbenzyloxy)-1-methyl-4-isopropyl-7-oxabicyclo[2.2.1]heptane, any of its individual enantiomers or any non-racemic mixture thereof can be accomplished by methods known in the art such as, for example, those described in EP 0 081 893 A2 and U.S. Pat. No. 4,487,945.

Thus, in a further aspect of the present invention, there is provided a process for preparing (±)-2-exo-(2-Methylbenzyloxy)-1-methyl-4-isopropyl-7-oxabicyclo[2.2.1]heptane, any of its individual enantiomers or any non-racemic mixture thereof comprising the steps of:

-   -   (i) preparing terpinolene epoxide of formula (IIa) (preferably         limonene-4-ol, more preferably terpinene-4-ol) as described         herein, and     -   (ii) converting terpinolene epoxide of formula (IIa) (preferably         limonene-4-ol, more preferably terpinene-4-ol) into         (±)-2-exo-(2-Methylbenzyloxy)-1-methyl-4-isopropyl-7-oxabicyclo[2.2.1]heptane,         any of its individual enantiomers or any non-racemic mixture         thereof.

The invention is illustrated by the following examples without being limited thereto or thereby.

EXAMPLE 1 Epoxidation of Terpinolene in Toluene with 1.8 eq Acetic Anhydride Using Sodium Acetate as Buffering Agent at 30° C.

148.5 g (1.0 mol) terpinolene (91.7%), 200 g (2.17 mol) toluene, 183.7 g (1.8 mol) acetic anhydride and 14.4 g (0.18 mol) sodium acetate were placed in a 1 L glass reactor and heated up to 30° C. After that 85.0 g (1.25 mol) H₂O₂ (50%) was dosed continuously under vigorous stirring over 3 h at 30° C. to the reaction mixture. The reaction mixture was stirred for further 1 h at 30° C. After addition of 50 g water and 100 g (1.08 mol) toluene the reaction mixture was cooled to 20° C. After phase split the water phase was extracted with 50 g (0.54 mol) toluene. The collected organic phases were washed with 35.5 g sodium sulfite solution (20% in water) at 20° C. to remove the peroxide. The organic phase was washed with twice with 100 g water and with 10% NaOH solution. The solvent of the organic phase was distilled off under reduced pressure (40° C.; 20 mbar).

Distillation residue: 183.4 g (raw epoxide)

Quantitative GC (gas chromatography): 61.4% w/w terpinolene oxide (content of residual terpinolene: 1.3 w/w %)

Yield: 74.0%

EXAMPLE 2 Epoxidation of Terpinolene in Toluene with 1.8 eq Acetic Anhydride Using Sodium Acetate as Buffering Agent at 15° C.

148.5 g (1.0 mol) terpinolene (91.7%), 200 g (2.17 mol) toluene, 183.7 g (1.8 mol) acetic anhydride and 14.4 g (0.18 mol) sodium acetate were placed in a 1 L glass reactor and cooled up to 15° C. After that 85.0 g (1.25 mol) H₂O₂ (50%) was dosed continuously under vigorous stirring over 3 h at 15° C. to the reaction mixture. The reaction mixture was stirred for further 1 h at 15° C. After addition of 50 g water and 100 g (1.08 mol) toluene the reaction mixture was cooled to 15° C. After phase split the water phase was extracted with 50 g (0.54 mol) toluene. The collected organic phases were washed with 35.5 g sodium sulfite solution (20% in water) at 15° C. to remove the peroxide. The organic phase was washed with twice with 100 g water and with 10% NaOH solution. The solvent of the organic phase was distilled off under reduced pressure (40° C.; 20 mbar).

Distillation residue: 183.4 g (raw epoxide)

Quantitative GC: 60.1% w/w terpinolene oxide (content of residual terpinolene: 8.4 w/w %)

Yield: 72.4%

EXAMPLE 3 Epoxidation of Terpinolene in Toluene with 1.4 eq Acetic Anhydride Using Sodium Acetate as Buffering Agent at 20° C.

146.5 g (1.0 mol) terpinolene (93%), 200 g (2.17 mol) toluene, 142.9 g (1.4 mol) acetic anhydride and 28.9 g (0.35 mol) sodium acetate were placed in a 1 L glass reactor and heated up to 30° C. After that 85.0 g (1.25 mol) H₂O₂ (50%) was dosed continuously under vigorous stirring over 3 h at 30° C. to the reaction mixture. The reaction mixture was stirred for further 1 h at 30° C. After addition of 50 g water and 100 g (1.08 mol) toluene the reaction mixture was cooled to 20° C. After phase split the water phase was extracted with 50 g (0.54 mol) toluene. The collected organic phases were washed with 35.5 g sodium sulfite solution (20% in water) at 20° C. to remove the peroxide. The organic phase was washed with twice with 100 g water and with 10% NaOH solution. The solvent of the organic phase was distilled off under reduced pressure (40° C.; 20 mbar).

Distillation residue: 196.1 g (raw epoxide)

Quantitative GC: 55.7% w/w terpinolene oxide (content of residual terpinolene: 4.0 w/w %)

Yield: 71.7%

EXAMPLE 4 Epoxidation of Terpinolene in Toluene with 1.2eq Acetic Anhydride Using Sodium Acetate as Buffering Agent at 20° C.

146.5 g (1.0 mol) terpinolene (93%), 200 g (2.17 mol) toluene, 122.5 g (1.2 mol) acetic anhydride and 28.9 g (0.35 mol) sodium acetate were placed in a 1 L glass reactor and heated up to 30° C. After that 85.0 g (1.25 mol) H₂O₂ (50%) was dosed continuously under vigorous stirring over 3 h at 30° C. to the reaction mixture. The reaction mixture was stirred for further 1 h at 30° C. After addition of 50 g water and 100 g (1.08 mol) toluene the reaction mixture was cooled to 20° C. After phase split the water phase was extracted with 50 g (0.54 mol) toluene. The collected organic phases were washed with 35.5 g sodium sulfite solution (20% in water) at 20° C. to remove the peroxide. The organic phase was washed with twice with 100 g water and with 10% NaOH solution. The solvent of the organic phase was distilled off under reduced pressure (40° C.; 20 mbar).

Distillation residue: 173.4 g (raw epoxide)

Quantitative GC: 62.6% w/w terpinolene oxide (content of residual terpinolene: 6.2 w/w %)

Yield: 71.3%

EXAMPLE 5 Epoxidation of Terpinolene in Toluene with 1.4 eq Acetic Anhydride Using Potassium Acetate as Buffering Agent at 20° C.

146.5 g (1.0 mol) terpinolene (93%), 200 g (2.17 mol) toluene, 142.9 g (1.4 mol) acetic anhydride and 34.6 g (0.35 mol) potassium acetate were placed in a 1 L glass reactor and heated up to 30° C. After that 85.0 g (1.25 mol) H₂O₂ (50%) was dosed continuously under vigorous stirring over 3 h at 30° C. to the reaction mixture. The reaction mixture was stirred for further 1 h at 30° C. After addition of 50 g water and 100 g (1.08 mol) toluene the reaction mixture was cooled to 20° C. After phase split the water phase was extracted with 50 g (0.54 mol) toluene. The collected organic phases were washed with 35.5 g sodium sulfite solution (20% in water) at 20° C. to remove the peroxide. The organic phase was washed with twice with 100 g water and with 10% NaOH solution. The solvent of the organic phase was distilled off under reduced pressure (40° C.; 20 mbar).

Distillation residue: 172.1 g (raw epoxide)

Quantitative GC: 63.6% w/w terpinolene oxide (content of residual terpinolene: 4.4 w/w %) Yield: 71.9%

EXAMPLE 6 Epoxidation of Terpinolene in Toluene with 1.2 eq Acetic Anhydride Using Sodium Acetate as Buffering Agent at 20° C.

150.3 g (1.0 mol) terpinolene (90.5%), 415 g (4.50 mol) toluene, 122.5 g (1.2 mol) acetic anhydride and 29.0 g (0.35 mol) sodium acetate were placed in a 1.6 L glass reactor and heated up to 20° C. After that 85.0 g (1.25 mol) H₂O₂ (50%) was dosed continuously under vigorous stirring over 3 h at 20° C. to the reaction mixture. The reaction mixture was stirred for further 4 h at 20° C. After addition of 50 g water and 100 g (1.08 mol) toluene the reaction mixture was cooled to 20° C. After phase split the water phase was extracted with 50 g (0.54 mol) toluene. The collected organic phases were washed with 30.0 g sodium sulfite solution (10% in water) at 20° C. to remove the peroxide. The organic phase was washed with twice with 100 g water and with 10% NaOH solution. The solvent of the organic phase was distilled off under reduced pressure (40° C.; 20 mbar).

Distillation residue: 253.1 g (raw epoxide)

Quantitative GC: 46.3% w/w terpinolene oxide (content of residual terpinolene: 2.3 w/w %)

Yield: 77.0% 

1-20. (canceled)
 21. A process for the epoxidation of a tetrasubstituted alkene to the corresponding epoxide comprising reacting the tetrasubstituted alkene with peracetic acid prepared in situ from acetic anhydride and hydrogen peroxide in the presence of at least one buffering agent wherein the hydrogen peroxide is used as an aqueous solution and the reaction is carried out in the presence of at least one inert organic solvent selected from non-halogenated aromatic hydrocarbons.
 22. The process of claim 21, wherein the buffering agent is selected from the group consisting of salts of inorganic acids, salts of organic acids and any combination thereof.
 23. The process of claim 21, wherein the buffering agent is a salt selected from the group consisting of phosphates, formates, acetates, carbonates, citrates, sulfates and any combination thereof.
 24. The process claim 21, wherein the buffering agent is selected from the group consisting of alkali metal and alkaline earth metal phosphates, alkali metal and alkaline earth metal acetates, alkali metal and alkaline earth metal carbonates and any combination thereof.
 25. The process of claim 21, wherein the molar ratio of hydrogen peroxide to acetic anhydride is from 2.0:1.9 to 1.1:1.05.
 26. The process of claim 21, wherein the temperature is from 0 to 50° C.
 27. The process of claim 21, wherein the tetrasubstituted alkene contains at east one additional carbon-carbon double bond.
 28. The process of claim 21, wherein the tetrasubstituted alkene is terpinolene of the formula (Ia)

and the corresponding epoxide is terpinolene epoxide of formula (IIa)


29. The process of claim 28, wherein the terpinolene epoxide of formula (IIa) is further converted via limonene-4-ol to terpinene-4-ol.
 30. The process of claim 28, wherein the terpinolene epoxide of formula (IIa), limonene-4-ol or terpinene-4-ol is further converted into (±)-2-exo-(2-Methylbenzyloxy)-1-methyl-4-isopropyl-7-oxabicyclo[2.2.1]heptane, any of its individual enantiomers or any non-racemic mixture thereof. 